Why do companies offer early retirement incentives? Wouldn't it be cheaper to wait until the day(or week or month) that you'd otherwise offer them to leave on, and fire them right then without any benefits? Especially since the stated purpose of it is to save money.
Ford in particular would probably get some negative PR. And since the most expensive employees are older, they might try to sue you for age discrimination. Is it just risk mitigation, or does Ford actually benefit from the incentive? 10% might be too large of a change to do all at once, especially at Ford's size; so buying them off lets them get rid of people gradually without surprising people.
I can understand why executives have to be bought off: They usually negotiate an accelerated stock vesting if they get fired without cause. What about anyone below that?